Pump

ABSTRACT

A pump includes a drive assembly having a drive shaft rotatable about a drive axis, and an eccentric coupled to the drive shaft for rotation therewith. The eccentric includes a shaft portion defining an eccentric axis that is offset from the drive axis. The shaft portion includes a shaft end defining a first alignment feature. A piston is rotatably coupled to the shaft portion and defines a second alignment feature. A cylinder reciprocatingly receives the piston. Positioning the first alignment feature in a predetermined orientation with respect to the second alignment feature locates the piston in one of a top-dead-center position and a bottom-dead-center position with respect to the cylinder.

BACKGROUND

The present invention relates to pumps, particularly to oil free pistonpumps and more particularly to an oil free piston pump suitable for usein medical applications.

Pumps are used for a variety of applications and in a variety ofenvironments. One type of pump is a dual piston pump having acentrally-located electric motor that drives more or less identicalpiston/cylinder assemblies mounted on each side of the motor. To providea consistent output and to balance the pump, the pistons of eachpiston/cylinder assembly are preferably out of phase with one anothersuch that when one piston is in a top-dead-center position, the otherpiston is in a bottom-dead-center position.

Like most industrial products, it is desirable to provide a pump that iseasy to assemble, low cost, durable, and that includes a minimal numberof parts.

SUMMARY

In one embodiment a pump includes a drive assembly including a driveshaft rotatable about a drive axis. An eccentric is coupled to the driveshaft for rotation therewith. The eccentric includes a shaft portiondefining an eccentric axis. The eccentric axis is offset from the driveaxis. The shaft portion includes a shaft end defining a first alignmentfeature. A piston is rotatably coupled to the shaft portion. The pistondefines a second alignment feature. A cylinder reciprocatingly receivesthe piston. Positioning the first alignment feature in a predeterminedorientation with respect to the second alignment feature locates thepiston in one of a top-dead-center position and a bottom-dead-centerposition with respect to the cylinder.

The pump can be configured such that first alignment feature includes atleast one of a projection extending from the shaft end and a recessformed in the shaft end. The second alignment feature can include twoalignment features and a plane extending through the two alignmentfeatures of the second alignment feature. The first alignment featurecan include at least one side, and the predetermined orientation caninclude wherein the plane is substantially parallel with the at leastone side. The predetermined orientation can also include wherein theplane extends through the first alignment feature. The first alignmentfeature can include at least one side, and the predetermined orientationcan include wherein the plane is oriented at a predetermined angle withrespect to the side.

The second alignment feature can include at least one of an opening anda projection. The first alignment feature can be a projection extendingfrom the shaft end and including two parallel sides, and the secondalignment feature can be a pair of diametrically opposed openings formedin an end face of the piston and a plane extending through thediametrically opposed openings. The pump can be configured such thatwhen the plane is substantially parallel to the two parallel sides, thepiston is in one of the top-dead-center position and the bottom-deadcenter position with respect to the cylinder. The projection can besubstantially rectangular and the openings can be substantiallycircular.

The drive shaft can include a first end to which the eccentric iscoupled, and a second end opposite the first end. The pump can alsoinclude a second eccentric coupled to the second end for rotationtherewith. The second eccentric can include a second shaft portiondefining a second eccentric axis. The second eccentric axis can beoffset from the drive axis, and the second shaft portion can include asecond shaft end defining a third alignment feature. The pump can alsoinclude a second piston rotatably coupled to the second shaft portion,where the second piston defines a fourth alignment feature. A secondcylinder can reciprocatingly receive the second piston, such thatpositioning the third alignment feature in the predetermined orientationwith respect to the fourth alignment feature locates the second pistonin one of a top-dead-center position and a bottom-dead-center positionwith respect to the second cylinder. When the piston is in thetop-dead-center position with respect to the cylinder, the second pistoncan be in the bottom-dead-center position with respect to the secondcylinder.

The first alignment feature can be non-circular. For example, the firstalignment feature can have a shape including one of a cross, oval,rectangle, polygon, triangle, teardrop, and star. The first alignmentfeature can also be circular and offset from the eccentric axis.

In other embodiments, a dual piston pump includes a first piston, asecond piston, a drive shaft having opposite ends, a first eccentric onone end of the drive shaft, and a second eccentric on an opposite end ofthe drive shaft. The first eccentric includes a shaft portion having afirst alignment feature. The first piston has a second alignmentfeature. The second eccentric includes a shaft portion having a thirdalignment feature, and the second piston has a fourth alignment feature.A method for orienting the first piston and the second piston in thedual piston pump includes mounting the first piston on the shaft portionof the first eccentric, rotating the first eccentric to position thefirst alignment feature in a first predetermined orientation withrespect to the second alignment feature, thereby locating the firstpiston in one of a top-dead-center position and a bottom-dead-centerposition, mounting the second piston on the shaft portion of the secondeccentric, rotating the second eccentric to position the third alignmentfeature in a second predetermined orientation with respect to the fourthalignment feature, thereby locating the second piston in the other ofthe top-dead-center position and the bottom-dead-center position,securing the first eccentric to the one end of the drive shaft toprevent relative rotation between the first eccentric and the driveshaft, and securing the second eccentric to the opposite end of thedrive shaft to prevent relative rotation between the second eccentricand the drive shaft.

Rotating the first eccentric to position the first alignment feature inthe first predetermined orientation can include engaging a firstalignment tool with the first alignment feature and the second alignmentfeature. The first alignment tool can include a first mating feature formating with the first alignment feature, and a second mating feature formating with the second alignment feature, and engaging the firstalignment tool can include mating the first mating feature with thefirst alignment feature and mating the second mating feature with thesecond alignment feature. Rotating the second eccentric to position thethird alignment feature in the second predetermined orientation caninclude engaging a second alignment tool with the third alignmentfeature and the fourth alignment feature. The second alignment featurecan include two alignment features and a plane extending through the twoalignment features of the second alignment feature, and rotating thefirst eccentric to position the first alignment feature in thepredetermined orientation with respect to the second alignment featurecan include positioning the first alignment feature such that the planeextends through the first alignment feature. The first alignment featurecan include at least one side, and the second alignment feature caninclude two alignment features and a plane extending through the twoalignment features of the second alignment feature, and rotating thefirst eccentric to position the first alignment feature in thepredetermined orientation with respect to the second alignment featurecan include orienting the side to be substantially parallel to theplane. Rotating the first eccentric to position the first alignmentfeature in the predetermined orientation with respect to the secondalignment feature can also include orienting the side at a predeterminedangle with respect to the plane.

In still other embodiments, a pump includes a motor including a motorhousing having a first end and a second end, a first crankcase coupledto the first end, a second crankcase coupled to the second end, a firstcylinder coupled to the first crankcase, a second cylinder coupled tothe second crankcase, a first valve body coupled to the first cylinder,and a second valve body formed separately from the first valve body andcoupled to the second cylinder. A first valve cover is coupled to thefirst valve body, and a second valve cover is formed separately from thefirst valve cover and is coupled to the second valve body. A connectingtube is formed separately from the first valve cover and the secondvalve cover and provides fluid communication between the first valvecover and the second valve cover.

The motor can include a motor housing, a stator within the motorhousing, and a rotor rotatably received within the stator. The rotor caninclude a drive shaft having a first end extending into the firstcrankcase and a second end extending into the second crankcase, and thedrive shaft can define a drive axis. The can also include a firsteccentric coupled to the first end and a second eccentric coupled to thesecond end, and each eccentric can include a shaft portion defining aneccentric axis offset from the drive axis, and a counterweight portionpositioned opposite the shaft portion with respect to the drive axis.The shaft portion of each eccentric can include a first alignmentfeature. A first piston can be received by the first cylinder androtatably coupled to the shaft portion of the first eccentric, and asecond piston can be received by the second cylinder and rotatablycoupled to the shaft portion of the second eccentric. Each of the firstpiston and the second piston can include a second alignment feature.When the first alignment feature of the first eccentric is in apredetermined orientation with respect to the second alignment featureof the first piston, the first piston can be in one of a top-dead-centerposition and a bottom-dead-center position, and the second piston can bein the other of the top-dead-center position and the bottom-dead-centerposition. When the first alignment feature of the first eccentric is inthe predetermined orientation with respect to the second alignmentfeature of the first piston, the first alignment feature of the secondeccentric can be in substantially the same predetermined orientationwith respect to the second alignment feature of the second piston.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a pump embodying the invention.

FIG. 2 is a front view of the pump of FIG. 1.

FIG. 3 is a back view of the pump of FIG. 1.

FIG. 4 is a left side view of the pump of FIG. 1.

FIG. 5 is a right side view of the pump of FIG. 1.

FIG. 6 is a top view of the pump of FIG. 1.

FIG. 7 is a bottom view of the pump of FIG. 1.

FIG. 8 is an exploded perspective view of the pump of FIG. 1.

FIG. 9. is a section view, shown in perspective, taken along line 4-4 ofFIG. 1.

FIG. 10 is an enlarged view showing a portion of the section view ofFIG. 4.

FIG. 11 is an elevational section view also taken along line 4-4 of FIG.1.

FIG. 12 is an enlargement of a portion of the section view of FIG. 11showing an end cap sealing arrangement for the pump of FIG. 1.

FIG. 13 is partially exploded perspective view of the pump of FIG. 1.

FIG. 14 is a partially exploded perspective view of the pump of FIG. 1.

FIG. 15 is an exploded perspective view of a valve assembly for the pumpof FIG. 1.

FIG. 16 is an alternate exploded perspective view of the valve assemblyof FIG. 15.

FIG. 17 is an enlargement of a portion of the section view of FIG. 11showing a valve body sealing arrangement for the valve assembly of FIG.15.

FIG. 18 is a perspective view of a piston assembly and piston alignmenttool for the pump of FIG. 1.

FIG. 19 is an alternate perspective view of the piston assembly andpiston alignment tool of FIG. 18.

FIG. 20 is a plan view of the piston alignment tool of FIG. 18.

FIG. 21 is a section view taken along line 21-21 of FIG. 20.

FIG. 22 is a perspective view of an alternative embodiment of the pistonassembly and piston alignment tool for the pump of FIG. 1.

FIG. 23 is an alternate perspective view of the piston assembly andpiston alignment tool of FIG. 22

FIG. 24 is a section view of a vent plug for the pump of FIG. 1.

It is to be understood that the invention is not limited in itsapplication to the details of the construction and the arrangements ofcomponents set forth in the following description or illustrated, in thedrawings. The present invention is capable of other embodiments and ofbeing practiced or being carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

FIGS. 1-7 illustrate a dual piston pump 10 embodying the invention. Thepump 10 includes a motor assembly 14, a first piston-cylinder assembly18 a positioned on one end of the motor assembly 14, and a secondpiston-cylinder assembly 18 b positioned on an opposite end of the motorassembly 14. For ease of manufacturing and commonality of parts, in theillustrated construction, the components of the first piston-cylinderassembly 18 a are substantially the same as the components of the secondpiston-cylinder assembly 18 b, and will therefore be identified by likereference numbers. Where appropriate, differences between the first andsecond piston-cylinder assemblies 18 a, 18 b will be specificallyidentified.

The motor assembly 14 includes a generally cylindrical motor housing 22.Each piston-cylinder assembly 18 a, 18 b includes a crankcase 26 coupledto the motor housing 22, a cylinder 30 coupled to the crankcase, a valvebody 34 coupled to the cylinder 30, and a valve cover 38 coupled to thevalve body 34 and securing the valve body 34 and the cylinder 30 to thecrankcase 26. The valve bodies 34 and valve covers 38 of each cylinderassembly 18 a, 18 b are formed separately from one another. While theillustrated motor assembly 14 is an electric motor, the pump could alsobe powered hydraulically, if desired.

Each crankcase 26 includes a plurality of outwardly extending ears 42,with the ears 42 of one crankcase 26 each defining a through bore 46,and the ears 42 of the other crankcase 26 each defining a threaded hole50. A plurality of elongated fasteners 54 extend between the crankcases26 and clamp the crankcases 26 against the ends of the motor housing 22.More specifically, each fastener 54 extends through the through bore 46of one of the crankcases 26, extends along the outside of the motorhousing 22, and is threaded into the threaded hole 50 of the othercrankcase 26. In alternative embodiments, both crankcases 26 may includethrough bores 46 and the fasteners 54 can be secured with nuts. In stillother embodiments, the crankcases can be snap fit onto the motor housing22 or can be secured to the motor housing 22 using clamps, twist-lockarrangements, or substantially any other suitable means of connection.

Each crankcase 26 defines a plurality of vent openings 58 adjacent themotor housing 22 to provide ventilation for the motor assembly 14. Eachcrankcase 26 also defines at least one (e.g., two, as illustrated)crankcase port 62 for intake or exhausting of the working fluid of thepump 10. The crankcases 26 also include generally cylindrical cylindersupports 66 that open into the crankcase 26 for supporting the cylinders30. Each cylinder support 66 includes a pair of diametrically opposedbosses 70 that define threaded bores 74 (see also FIG. 13). Fasteners 78extend through each valve cover 38 and valve body 34 and along the sidesof each cylinder 30, to couple the respective valve cover 38, valve body34, and cylinder 30 to the crankcase 26. The fasteners 78 are threadedinto the treaded bores 74 of the cylinder support bosses 70.

Referring also to FIGS. 8-11, the motor assembly 14 includes a stator 82fixedly mounted within the motor housing 22, and a rotor 86 rotatablyreceived within the stator 82. The rotor 82 includes a drive shafthaving a first end 90 extending into one of the crankcases 26 and asecond end 94 extending into the other of the crankcases 26. The driveshaft rotates about a drive axis 98 and is mounted in bearings 102supported by the crankcases 26.

Each of the first end 90 and the second end 94 of the drive shaft hascoupled thereto an eccentric 106. Each eccentric 106 includes a bore 110that receives the first end 90 or the second end 94. Each eccentric 106also includes a counterweight portion 114 positioned on one side of thedrive axis 98, and a shaft portion 118 positioned on an opposite side ofthe drive axis 98. In this regard, the counterweight portion 114 and theshaft portion 118 are diametrically opposed to one another with respectto the drive axis 98. The shaft portion 118 defines an eccentric axis122 that is substantially parallel to and offset from the drive axis 98.The shaft portion 118 also includes an alignment projection 124 thatextends axially from the distal end of the shaft portion 118. In theillustrated embodiment, the alignment projection 124 is generally in theform of a rectangle, but other shapes are also possible. The alignmentprojection 124 aids in proper assembly of the pump 10, as discussedfurther below.

When the drive shaft rotates, the counterweight portion 114 and theshaft portion 118 of each eccentric 106 revolve around the drive axis98. As shown in FIG. 11 and discussed further below, the eccentrics 106are coupled to the respective first and second ends 90, 94 so that whenthe counterweight portion 114 of one eccentric 106 is above the driveaxis 98, the counterweight portion 114 of the other eccentric 106 isbelow the drive axis 98.

Referring also to FIG. 12, each crankcase 26 includes an end opening 126that affords access to the interior of the crankcase 26 for assembly andmaintenance. During use, the end opening 126 of each crankcase iscovered by a crankcase cover 130. The crankcase cover 130 includes aninner, generally cylindrical wall 134 that fits within the end opening126, and an outer, generally annular wall 138 that abuts an end surface142 of the crankcase 26. The annular wall 138 includes a circumferentialgroove 146 that receives a resilient O-ring 150. In the illustratedembodiment, screws 154 are used to secure the crankcase cover 130 to thecrankcase 26. More specifically, the screws 154 extend through tabs 158on the crankcase cover 130 and screw into threaded bores 162 (FIG. 8)provided on the crankcase 26. In this way, when the screws 154 aretightened the crankcase cover 130 is drawn axially toward the crankcasesuch that the O-ring 150 is compressed between the end surface 142 ofthe crankcase 26 and the circumferential groove 146. Other embodimentsof the pump 10 can replace or supplement the screws 154 with varioustypes of clamping mechanisms, over-center mechanisms, ratchet mechanism,snap-fit configurations, and the like to provide an axial clamping forcethat draws the crankcase cover 130 snugly against the end surface 142.By axially compressing the O-ring 150, the resulting seal is lesssusceptible to leakage due to components expanding and contracting asthe pump 10 changes temperatures during operating cycles. This isparticularly true where the crankcase 26 and crankcase cover 130 areformed of materials having different thermal expansion properties. Forexample, in one embodiment the crankcase 26 is formed of metal and thecrankcase cover 130 is formed from plastic.

Referring also to FIGS. 13-14, a piston 166 is rotatably coupled to theshaft portion 118 of each eccentric 106. Each piston 166 includes afirst, disk-like sealing portion 170 that is received by the cylinder30, an elongated connecting portion 174 extending from the first portion170, and a generally annular second portion 178 that is coupled to theshaft portion 118. A bearing 182 is pressed into the second portion 178and pressed over the shaft portion 118 to rotatably couple the piston166 to the eccentric 106.

The second portion 178 of the piston 166 includes a generally annularend face 186 that faces toward the end opening 126 when the pistons 166are installed in their respective crankcases 26. The end face 186defines a pair of alignment apertures in the form of diametricallyopposed bores 190. The bores 190 are oriented along a plane P (FIG. 14)that is substantially perpendicular to the longitudinal extent of theelongated connecting portion 174. The bores 190 can be blind bores orcan be through bores.

As best shown in FIG. 10, the first portion 170 of the piston 166includes a top surface 192, a bottom surface 193 opposite the topsurface 192, and an outer perimeter defining a shoulder 194 forreceiving a sealing member. The sealing member includes a resilientportion 198 having a generally L-shaped cross-section and engaging aninner wall 202 of the cylinder 30, and a substantially rigid ring-likeportion 206 that secures the resilient portion 198 against the shoulder194 of the piston 166. When the piston 166 is installed in the cylinder30 and the valve body 34 is installed on the cylinder 30, the piston 166and the valve body 34 cooperate to define a chamber 208 having a volumethat changes as the piston 166 moves up and down in the cylinder 30. Thefirst portion 170 also defines a valve opening 210 that extends throughthe first portion 170 between the top and bottom surfaces 192, 193, andthat is located between the center of the first portion 170 (e.g.,approximately where the elongated connecting portion 174 connects to thefirst portion 170) and the shoulder 194.

A first reed valve 214 includes a fixed portion 216 coupled to thecenter of the first portion 170 by a screw 218, and a moveable portion222 that overlies the valve opening 210. The first reed valve 214 isflexible such that when the pressure on the bottom surface 193 of thepiston 166 is greater than the pressure on the top surface 192 of thepiston 166, as occurs, for example, when the piston 166 moves downwardlyin the cylinder 30, the first reed valve 214 flexes upwardly such thatthe moveable portion 222 moves away from the valve opening 210 and theworking fluid of the pump is allowed to flow through the valve opening210. In contrast, when the pressure on the top surface 192 of the piston166 is greater than the pressure on the bottom surface 193 of the piston166, as occurs, for example, when the piston 166 moves upwardly in thecylinder 30, the moveable portion 222 is urged against the valve opening210 and thus prevents the flow of working fluid through the valveopening 210. A small groove 224 is formed in the top surface 192 andextends below the reed valve 214 where the moveable portion 222 meetsthe fixed portion 216 to relieve bending stresses on the reed valve 214.Although reed valve 214 is shown as controlling the flow of workingfluid past the first portion 170 of the piston 166, those skilled in theart will readily appreciate that other valve types can also be used.

FIGS. 15-17 show details of the valve body 34 and valve cover 38. Asnoted above, the valve body 34 and valve cover 38 are coupled to thecylinder 30 and crankcase 26 by the fasteners 78. More specifically, thevalve body 34 includes a pair of diametrically opposed ears 226, andeach ear 226 defines a through hole 230 that receives one of thefasteners 78. The valve cover 38 also includes a pair of diametricallyopposed ears 234 that also define through holes 238 for receiving thefasteners 78. The fasteners 78 both align the valve body 34 and thevalve cover 38 with one another and with the cylinder 30 and secure thevalve body 34, the valve cover 38, and the cylinder 30 to the crankcase26.

The valve body 34 includes an upper flange portion 242 having an outerdiameter similar to that of the cylinder 30. A reduced-diameter insertportion 246 extends axially from the flange portion 242 and has an outerdiameter sized to snugly fit within the cylinder 30. As best shown inFIG. 17, the insert portion 246 defines a radially-outwardly facingcircumferential groove 250 that receives a first sealing O-ring 254. Theflange portion 242 defines an axially-facing circumferential groove 258that receives a second sealing O-ring 262. When the insert portion 246is inserted into the cylinder 30, the first O-ring 254 is compressedbetween the groove 250 and the inner wall 202 of the cylinder 30 toprovide an air-tight seal between the valve body 34 and the cylinder 30.Similarly, when the valve cover 38 is tightened against the valve body34, the second O-ring 262 is compressed between the groove 258 and abottom surface 266 of the valve body 34 (see also FIG. 16) to provide anair-tight seal between the valve body 34 and the valve cover 38.

As best shown in FIGS. 10, 15, and 16, the valve body 34 defines acentrally-located valve opening 270 extending through the valve body 34from a first side 274 of the valve body 34 that faces the piston 166 toa second side 278 of the valve body 34 that faces the valve cover 38. Asecond reed valve 282 is coupled to the second side 278 of the valvebody 34 and includes a fixed portion 286 coupled to the second side 278by a screw 290, and a moveable portion 294 that overlies the valveopening 270. The second reed valve 282 is flexible such that when thepressure on the first side 274 of the valve body 34 is greater than thepressure on the second side 278 of the valve body 34, as occurs, forexample, when the piston 166 moves upwardly in the cylinder 30, thesecond reed valve 282 flexes upwardly such that the moveable portion 294moves away from the valve opening 270 and the working fluid of the pumpis allowed to flow through the valve opening 270. In contrast, when thepressure on the second side 278 of the valve body 34 is greater than thepressure on the first side 274 of the valve body 34, as occurs, forexample, when the piston 166 moves downwardly in the cylinder 30, themoveable portion 294 is urged against the valve opening 270 and thusprevents the flow of working fluid through the valve opening 270.Although reed valve 282 is shown as controlling the flow of workingfluid past the valve body 34, those skilled in the art will readilyappreciate that other valve types can also be used.

The valve cover 38 cooperates with the valve body 34 to define a chamber298. In the illustrated embodiment, the chamber 298 is a pressurechamber that is pressurized during operation of the pump 10 as discussedfurther below. The valve cover 38 includes a substantially cylindricalouter wall 302 and a flange portion 306 extending radially outwardlyfrom a bottom end of the outer wall 302. The flange portion 306 definesthe bottom surface 266 of the valve body that cooperates with the O-ring262 to provide the seal between the valve cover 38 and the valve body34. The valve cover 38 also includes a top wall 307 having a pluralityof elongated ribs 308 that function as heat sinks to help regulate thetemperature of the valve cover 38.

The valve cover 38 also includes a conduit portion 310 that extendsacross the middle of the valve cover 38, is oriented substantiallytransversely to the diametrically opposed ears 234, and thatsubstantially bisects the top wall 307. The conduit portion 310 includesan outlet port 314 on one end and a connection port 318 on the otherend. Both the outlet port 314 and the connection port 318 are incommunication with the chamber 298. The connection port 318 isconfigured to receive one end of a connection tube 322 that extendsbetween the two valve covers 38. The connection tube 322 includescircumferential grooves 326 at each end, which grooves 326 each receivean O-ring 330 to provide an air tight seal between the valve covers 38and the connection tube 322. The connection tube 322 affords fluidcommunication between the chambers 298 of each piston/cylinder assembly18 a, 18 b.

In the illustrated embodiment, the outlet port 314 of one of the valvecovers 38 is tapped so that a threaded pressure release valve 334 can beinserted therein. The other outlet port 314 is illustrated as having asmooth inner surface for receiving a connector or coupler for attachmentto other equipment, but could also be threaded depending upon thespecific application.

FIGS. 19-22 illustrate the piston 166 and the eccentric 106 along withan alignment tool 338 that is used during assembly or installation ofthe eccentric 106 and piston 166 to the drive shaft. As mentioned above,the end of the shaft portion 118 includes an alignment projection 124that extends outwardly from the shaft portion 118. Also, bores 190 areformed in the annular end face 186 of the piston 166. In the illustratedconstruction, the alignment projection 124 is substantially rectangularand includes a pair of substantially parallel sides 342. The alignmenttool 338 is substantially disk shaped and defines a first mating featurein the form of a substantially rectangular slot or alignment recess 346that receives the alignment projection 124, and second mating feature inthe form of a pair of substantially circular alignment projections orpins 350 that extend into and are received by the bores 190 in thepiston 166. As best shown in FIGS. 18 and 20, the alignment recess 346and pins 350 are substantially co-planar. As such, when the alignmenttool 338 is engaged with the assembled piston 166 and eccentric 106, thealignment tool 338 aligns the parallel sides 342 of the alignmentprojection 124 with the bores 190 such that the plane P extendingthrough the bores 190 is substantially parallel with the sides 342. Whenthe eccentric 106 and piston 166 are located in this predeterminedorientation, the piston will be in either a top-dead-center position ora bottom-dead center position. As shown in FIGS. 18 and 19, theeccentric 106 includes a set screw 354 that extends into the bore 110 sothat when the set screw 354 is loosened the eccentric 106 can be rotatedwith respect to the first or second end 90, 94 of the drive shaft andwhen the set screw 354 is tightened the eccentric 106 is fixed forrotation with the first or second end 90, 94 of the drive shaft. Asunderstood by those skilled in the art, the top-dead-center position andthe bottom-dead-center positions are the two positions in which thelongitudinal extent of the piston 166 is aligned with a plane defined bythe drive axis 98 and the eccentric axis 122. During operation of thepump, the top-dead-center position and the bottom-dead-center positionrepresent the moment in time when the piston 166 reverses its directionof movement in the cylinder.

During installation of the pistons 166 for manufacturing or repair ofthe pump 10, two alignment tools 338 are used to position one of thepistons 166 in the top-dead-center position and the other of the pistons166 in the bottom-dead-center position. For example, as shown in FIG.11, the piston 166 on the right in the piston/cylinder assembly 18 a isin the bottom-dead-center position and the piston 166 on the left in thepiston/cylinder assembly 18 b is in the top-dead-center position.Although the steps can be performed in various sequences, in oneexemplary method of assembly, a first piston 166 and its bearing 182 areinstalled onto the shaft portion 118 of a first eccentric 106, and asecond piston 166 and its bearing 182 are installed onto the shaftportion 118 of a second eccentric. A first alignment tool 338 is thenengaged with the first eccentric 106 and the first piston 166 to holdthe first piston 166 in one of the top-dead-center position or thebottom-dead-center position. A second alignment tool 338 is then engagedwith the second eccentric 106 and the second piston 166 to hold thesecond piston 166 in the other of the top-dead-center position and thebottom-dead-center position.

Each eccentric 106, piston 166, and alignment tool 338 combination canthen be inserted into the crankcase 24 through the opening defined by arespective one of the cylinder supports 66. During this process thealignment tools 338 maintain the pistons 166 in the top-dead-center orbottom-dead-center orientation with respect to the eccentrics 106. Thebore 110 of each eccentric 106 is positioned over the respective firstor second end 90, 94 of the drive shaft and the respective set screws354 are tightened so that each eccentric 106 is coupled for rotationwith the drive shaft about the drive axis 98. As shown in FIG. 3, thecrankcase ports 62 are positioned to afford access to the set screws 354for tightening and loosening with an appropriate tool. Once the setscrews 354 have been tightened, the alignment tools 338 can bedisengaged from the eccentric 106 and the piston 166 and extracted fromthe crankcase 26 through the end openings 126.

In some situations, such as for adjustment when the eccentrics 106 arealready positioned on the ends 90, 94 of the drive shaft, the set screws354 can be kept loose or loosened and the alignment tools 338 can beinserted into the crankcase through the end openings 126. The eccentrics106 can then be rotated with respect to the drive shaft and thealignment tools 338 engaged with the respective eccentric 106 and piston166 to orient one of the pistons in the top-dead-center position and theother piston 166 in the bottom-dead-center position. Then, while thealignment tools 338 maintain the proper orientation of the pistons 166,the set screws 354 can be tightened such that the eccentrics 106 arecoupled for rotation with the drive shaft.

It should be appreciated that the present invention is not necessarilylimited to the specific configuration and relative placement of thealignment projection 124 and the bores 190 illustrated in the drawings.For example, instead of the alignment projection 124 the alignmentfeature of the eccentric 106 could be defined by a recess formed in theshaft portion 118, in which case the alignment tool 338 would include asuitable projection. The configuration of the bores 190 and the pins 350could similarly be reversed such that the piston 166 includes a pair ofpins or other protrusions and the alignment tool 338 includes a pair ofbores or openings. Moreover, the piston 166 could include only oneprojection, only one recess, or even one projection and one recess. Thespecific shapes of the alignment features can also vary. For example, ifthe alignment feature on the shaft portion 118 is substantially centeredon the eccentric axis 122, the alignment feature could be substantiallyany non-circular or polygon shape, such as a square, star, cross, oval,pentagon, triangle, teardrop, or star, without limitation. The alignmentfeature on the shaft portion 118 could also be offset with respect tothe eccentric axis 122, in which case a circular or non-circular shapewould be suitable and capable of orienting the eccentric 106 and thepiston 166 relative to one another. The bores 190 and pins 350 couldsimilarly be formed of any variety of shapes, provided that thecombination chosen is sufficient to locate the pistons 166 in one of thetop-dead-center and bottom-dead-center locations.

By way of example only, FIGS. 22 and 23 illustrate an alternativeembodiment in which the second alignment features or bores 190 have beenpositioned differently on the piston 166. In FIGS. 22 and 23, the bores190 are again located on the end face 186 of the piston 190, but itshould be appreciated that the bores 190 or any other alignment featurescould also be located on the connecting portion 174. As before, a planeP extends through the bores 190 and provides a reference for determiningthe predetermined orientation of the bores 190 relative to the firstalignment feature or projection 124 of the eccentric 106. In the exampleof FIGS. 22 and 23, the predetermined orientation for locating thepiston 190 in either the top-dead-center or bottom-dead-center locationinvolves locating projection 124 at a predetermined angle with respectto the plane P. More specifically, at least one of the sides 342 of theprojection 124 is oriented at a predetermined angle with respect to theplane P. As best shown in FIG. 22, the alignment tool 338 is alsoconfigured differently in a manner corresponding to the differentconfiguration of the bores 190. More specifically, the pins orprojections 350 on the alignment tool 338 are reoriented such that whenthe pins 350 are inserted into the bores 190 and recess 346 receives theprojection 124, the piston 166 is properly located in either thetop-dead-center or the bottom-dead-center location.

FIG. 24 illustrates a port insert in the form of a plug 358 that can beused for obstructing any of the crankcase ports 62, outlet ports 314, orconnection ports 318 to configure the pump in a particular way. In FIG.22 the plug 358 is shown obstructing one of the crankcase ports 62. Theplug 358 is generally cylindrical and includes a body 362 having areduced-diameter inner end 366 that is received within the port 62 andan enlarged-diameter outer end 370 that abuts a shoulder 374 defined bythe crankcase port 62. The inner end defines an inner circumferentialgroove 378 that receives a single sealing O-ring 382. When the plug 358is inserted into the port 62, the O-ring is compressed between thecircumferential groove 378 and the port 62 to provide the seal. An outercircumferential groove 386 is formed between the inner end 366 and theouter end 370 and partially defines a substantially annular andinwardly-facing engagement surface 390 that abuts the shoulder 374.Although the illustrated port insert is the plug 358, similarlyconfigured port inserts can also be provided for coupling external fluidlines to the pump 10. By way of example only, a wide variety of portinserts having, among other things, threaded extension, barbedconnection, 90-degree or −45 degree elbows, and the like can be providedfor connecting the pump 10 to external equipment.

With reference primarily to FIGS. 9-11, in operation, the illustratedpump 10 is configured to draw working fluid into the crankcases 26 byway of the crankcase ports 62 and compress the working fluid in thechambers 208, thereby forcing working fluid into the chambers 298 andproviding a high-pressure output of working fluid at the outlet port314. Referring to the piston/cylinder assembly 18 b, and starting withthe piston 166 in the top-dead-center position (as illustrated), whenthe motor assembly 14 operates and rotates the stator 86, the first end90 of the drive shaft rotates the eccentric 106 about the drive axis 98.As the eccentric 106 rotates about the drive axis 98, the piston 166begins moving downwardly within the cylinder 30. As the piston 166 movesdownwardly the volume of the chamber 208 begins to increase, creating anet negative pressure within the chamber 208.

At the second reed valve 282, the negative pressure within the chamber208 draws the flexible portion 294 tightly against the second side 278of the valve body 34, thereby blocking flow through the valve opening270. Substantially simultaneously, the negative pressure within thechamber 208 opens the first reed valve 214 by bending the flexibleportion 222 of the first reed valve 214 away from the top surface 192 ofthe sealing portion 170 of the piston 166, thereby allowing workingfluid to flow into the chamber 208 by way of the valve opening 210. Flowof working fluid through the valve opening 210 and into the chamber 208generally continues until the piston 166 reaches the bottom-dead-centerposition, at which point the piston 166 reverses direction and beginsmoving upwardly in the cylinder 30.

As the piston 166 rises in the cylinder, the pressure in the chamber 208begins to increase. As a result, the flexible portion 222 of the firstreed valve 214 is pressed against the top surface 192 of the piston,thus closing the first reed valve 214 and preventing fluid flow throughthe valve opening 210. Substantially simultaneously, the increasingpressure in the chamber 208 bends the flexible portion 294 of the secondreed valve 282 away from the second side 278 of the valve body 34, thusopening the second reed valve 282 and allowing pressurized working fluidto flow into the chamber 298 through the valve opening 270. Eventuallythe piston 166 reaches top-dead-center again and the cycle repeats.While this is going on, the same cycle occurs with the piston 166 of thepiston/cylinder assembly 18 a, however when the piston 166 of thepiston/cylinder assembly 18 b is moving upwardly in the cylinder 30, thepiston 166 of the piston/cylinder assembly 18 a is moving downwardly inthe cylinder 30.

As previously mentioned, the pistons 166 of the piston/cylinderassemblies 18 a, 18 b are arranged such that when one is in thetop-dead-center position the other is in the bottom-dead-centerposition. As a result, except for the very brief moments when bothpistons 166 are at either top-dead-center or bottom-dead-center and arethus stationary in their respective cylinders 30, there is always onecylinder forcing working fluid into the chamber 298 to maintain a moreconsistent pressure output.

In the illustrated embodiment, the pressurized working fluid isdischarged by way of the outlet port 314 in the piston/cylinder assembly18 a. The pressure release valve 334 in the outlet port 314 of thepiston/cylinder assembly 18 b prevents excessive pressure from buildingup within the chambers 298. The connecting tube 322 allows pressurizedworking fluid to flow from the chamber 298 of the piston/cylinderassembly 18 b to the chamber 298 of the piston/cylinder assembly 18 a.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A pump comprising: a drive assembly including adrive shaft rotatable about a drive axis; an eccentric coupled to thedrive shaft for rotation therewith, the eccentric including a shaftportion defining an eccentric axis, the eccentric axis offset from thedrive axis, the shaft portion including a shaft end defining a firstalignment feature; a piston rotatably coupled to the shaft portion, thepiston defining a second alignment feature; and a cylinderreciprocatingly receiving the piston, wherein positioning the firstalignment feature in a predetermined orientation with respect to thesecond alignment feature locates the piston in one of a top-dead-centerposition and a bottom-dead-center position with respect to the cylinder.2. The pump of claim 1, wherein the first alignment feature includes atleast one of a projection extending from the shaft end and a recessformed in the shaft end.
 3. The pump of claim 1, wherein the secondalignment feature includes two alignment features and a plane extendingthrough the two alignment features of the second alignment feature. 4.The pump of claim 3, wherein the first alignment feature includes atleast one side, and wherein the predetermined orientation includeswherein the plane is substantially parallel with the at least one side.5. The pump of claim 3, wherein the predetermined orientation includeswherein the plane extends through the first alignment feature.
 6. Thepump of claim 3, wherein the first alignment feature includes at leastone side, and wherein the predetermined orientation includes wherein theplane is oriented at a predetermined angle with respect to the side. 7.The pump of claim 1, wherein the second alignment feature includes atleast one of an opening and a projection.
 8. The pump of claim 1,wherein the first alignment feature is a projection extending from theshaft end and including two parallel sides, wherein the second alignmentfeature is a pair of diametrically opposed openings formed in an endface of the piston and a plane extending through the diametricallyopposed openings, and wherein when the plane is substantially parallelto the two parallel sides, the piston is in one of the top-dead-centerposition and the bottom-dead center position with respect to thecylinder.
 9. The pump of claim 8, wherein the projection issubstantially rectangular and wherein the openings are substantiallycircular.
 10. The pump of claim 1, wherein the drive shaft includes afirst end to which the eccentric is coupled, and a second end oppositethe first end, the pump further comprising: a second eccentric coupledto the second end for rotation therewith, the second eccentric includinga second shaft portion defining a second eccentric axis, the secondeccentric axis offset from the drive axis, the second shaft portionincluding a second shaft end defining a third alignment feature; asecond piston rotatably coupled to the second shaft portion, the secondpiston defining a fourth alignment feature; and a second cylinderreciprocatingly receiving the second piston, wherein positioning thethird alignment feature in the predetermined orientation with respect tothe fourth alignment feature locates the second piston in one of atop-dead-center position and a bottom-dead-center position with respectto the second cylinder.
 11. The pump of claim 10, wherein when thepiston is in the top-dead-center position with respect to the cylinder,the second piston is in the bottom-dead-center position with respect tothe second cylinder.
 12. The pump of claim 1, wherein the firstalignment feature is non-circular.
 13. The pump of claim 12, wherein thefirst alignment feature has a shape including one of a cross, oval,rectangle, polygon, triangle, teardrop, and star.
 14. The pump of claim1, wherein the first alignment feature is circular and is offset fromthe eccentric axis.
 15. A method for orienting a first piston and asecond piston in a dual piston pump, the pump including a drive shafthaving opposite ends, a first eccentric on one end of the drive shaft,and a second eccentric on an opposite end of the drive shaft, the firsteccentric including a shaft portion having a first alignment feature,the first piston having a second alignment feature, the second eccentricincluding a shaft portion having a third alignment feature, and thesecond piston having a fourth alignment feature, the method comprising:mounting the first piston on the shaft portion of the first eccentric;rotating the first eccentric to position the first alignment feature ina first predetermined orientation with respect to the second alignmentfeature, thereby locating the first piston in one of a top-dead-centerposition and a bottom-dead-center position; mounting the second pistonon the shaft portion of the second eccentric; rotating the secondeccentric to position the third alignment feature in a secondpredetermined orientation with respect to the fourth alignment feature,thereby locating the second piston in the other of the top-dead-centerposition and the bottom-dead-center position; securing the firsteccentric to the one end of the drive shaft to prevent relative rotationbetween the first eccentric and the drive shaft; and securing the secondeccentric to the opposite end of the drive shaft to prevent relativerotation between the second eccentric and the drive shaft.
 16. Themethod of claim 15, wherein rotating the first eccentric to position thefirst alignment feature in the first predetermined orientation includesengaging a first alignment tool with the first alignment feature and thesecond alignment feature.
 17. The method of claim 16, wherein the firstalignment tool includes a first mating feature for mating with the firstalignment feature, and a second mating feature for mating with thesecond alignment feature, and wherein engaging the first alignment toolincludes mating the first mating feature with the first alignmentfeature and mating the second mating feature with the second alignmentfeature.
 18. The method of claim 16, wherein rotating the secondeccentric to position the third alignment feature in the secondpredetermined orientation includes engaging a second alignment tool withthe third alignment feature and the fourth alignment feature.
 19. Themethod of claim 15, wherein the second alignment feature includes twoalignment features and a plane extending through the two alignmentfeatures of the second alignment feature, and wherein rotating the firsteccentric to position the first alignment feature in the predeterminedorientation with respect to the second alignment feature includespositioning the first alignment feature such that the plane extendsthrough the first alignment feature.
 20. The method of claim 15, whereinthe first alignment feature includes at least one side, wherein thesecond alignment feature includes two alignment features and a planeextending through the two alignment features of the second alignmentfeature, and wherein rotating the first eccentric to position the firstalignment feature in the predetermined orientation with respect to thesecond alignment feature includes orienting the side to be substantiallyparallel to the plane.
 21. The method of claim 15, wherein the firstalignment feature includes at least one side, wherein the secondalignment feature includes two alignment features and a plane extendingthrough the two alignment features of the second alignment feature, andwherein rotating the first eccentric to position the first alignmentfeature in the predetermined orientation with respect to the secondalignment feature includes orienting the side at a predetermined anglewith respect to the plane.
 22. A pump comprising: a motor including amotor housing having a first end and a second end; a first crankcasecoupled to the first end; a second crankcase coupled to the second end;a first cylinder coupled to the first crankcase; a second cylindercoupled to the second crankcase; a first valve body coupled to the firstcylinder; a second valve body formed separately from the first valvebody and coupled to the second cylinder; a first valve cover coupled tothe first valve body; a second valve cover formed separately from thefirst valve cover and coupled to the second valve body; and a connectingtube formed separately from the first valve cover and the second valvecover and providing fluid communication between the first valve coverand the second valve cover.
 23. The pump of claim 22, wherein the motorincludes a motor housing, a stator within the motor housing, and a rotorrotatably received within the stator, the rotor including a drive shafthaving a first end extending into the first crankcase and a second endextending into the second crankcase, the drive shaft defining a driveaxis.
 24. The pump of claim 22, further comprising a first eccentriccoupled to the first end and a second eccentric coupled to the secondend, each eccentric including a shaft portion defining an eccentric axisoffset from the drive axis, and a counterweight portion positionedopposite the shaft portion with respect to the drive axis.
 25. The pumpof claim 24, wherein the shaft portion of each eccentric includes afirst alignment feature.
 26. The pump of claim 25, further comprising afirst piston received by the first cylinder and rotatably coupled to theshaft portion of the first eccentric, and a second piston received bythe second cylinder and rotatably coupled to the shaft portion of thesecond eccentric, each of the first piston and the second pistonincluding a second alignment feature.
 27. The pump of claim 26, whereinwhen the first alignment feature of the first eccentric is in apredetermined orientation with respect to the second alignment featureof the first piston, the first piston is in one of a top-dead-centerposition and a bottom-dead-center position, and the second piston is inthe other of the top-dead-center position and the bottom-dead-centerposition.
 28. The pump of claim 27, wherein when the first alignmentfeature of the first eccentric is in the predetermined orientation withrespect to the second alignment feature of the first piston, the firstalignment feature of the second eccentric is in substantially the samepredetermined orientation with respect to the second alignment featureof the second piston.